1. Field of the Invention
The present invention relates to image-data processing apparatuses, image-data processing methods, and imaging systems with which frame flicker, which occurs, for example, in high-speed imaging, is corrected. More specifically, the present invention relates to an image-data processing apparatus, an image-data processing method, and an imaging system with which a correction gain for each frame is calculated on the basis of an integrated value of the frame, obtained by integrating pixel data in a selected range having either values greater than or equal to a threshold or values less than or equal to the threshold, and the values of the pixel data in the selected range of the frame are corrected on the basis of the correction gain, so that the load of processing for determining the correction gain can be reduced, and so that flicker in an image region corresponding to the pixel data in the selected range can be corrected appropriately.
2. Description of the Related Art
The problem of flicker is considered to be significant particularly in the case of a rolling-shutter (focal-plane-shutter) imaging device. However, also in the case of a global-shutter imaging device, light tends to flicker over the entire screen, i.e., frame flicker occurs, in high-speed imaging due to the imaging rate being faster than the ON/OFF period of illumination. In some cases, the frame flicker makes it difficult to correct individual regions in the screen due to difference in the phase or level of illumination among the individual region, for example, when a plurality of light sources exists in the image on the screen.
In an existing method of flicker correction, a region where flicker has occurred is detected and correction is executed in the region. With this method, detection is to be executed as to in which region flicker has occurred. However, the status of flicker varies depending on light sources or objects, so that processing for detecting a region becomes complex and the load increases in order to achieve accurate correction.
In another existing method of flicker correction, a correction gain is determined on the basis of an average value and an integrated value of a frame. With this method, if regions of different flicker states (e.g., regions where flicker has occurred and regions where flicker has not occurred) exist in the screen, when correction is executed in the regions where flicker has occurred, conversely, flicker newly occurs in the regions where flicker had not occurred.
In a first example of flicker correction, shown in FIG. 8, a rectangular parallelepiped occupies a large ratio among components in a frame. Thus, when flicker components of the rectangular parallelepiped are corrected, flicker components occur in a background due to the correction gain. Conversely, in a second example of flicker correction, shown in FIG. 9, a background occupies a large ratio among components in a frame. Thus, when flicker components of the background are corrected, flicker components occur in a rectangular parallelepiped due to the correction gain.
According to techniques proposed in Japanese Unexamined Patent Application Publication No. 2000-101909, a screen is divided into regions, flicker correction gains are calculated for the individual divided regions, and flicker correction is executed in the divided regions independently using their individual flicker correction gains.